I think the original comment is partially a joke. Maybe there isn't specifically anything wrong with this, but there is the fact that it is written in C. Historically there is a good precedent of this being an issue. C does not guarantee correctness to the same level as more modern languages.
If it was written in Haskell or Rust for example you could be more sure about correctness. I believe for something like this, correctness is fairly important. Not to mention you probably wont even lose speed. As for if the code is understandable, it is a 2600 lines of terse-ish C [0]. Do you really think about the entire blob at the same time?